Before his 6-under-par 66 in Friday’s British Open second round at Royal Liverpool — that followed his opening-round 66 and has him at 12-under par with a four-shot lead entering the weekend — McIlroy’s season had been defined by his Friday foibles.

You may have read these statistics recited a few times: In 14 events this season, he had taken 60 more shots in his Friday rounds than his Thursday rounds. In PGA Tour events, he was averaging 68.0 on Thursdays, ranked first, and 72.9 on Fridays, ranked 181st.

Most recently, at last week’s Scottish Open, he shot a course-record 64 at Royal Aberdeen and followed it with a 78 on Friday.

This time on Friday, McIlroy backed his Thursday round up and has a similar look to the ones he had when he was winning his first two major championships in eight-shot runaways.

McIlroy, like Tiger Woods in his heyday, has proven to be a world-class front-runner — as evidenced by his two blowout wins at majors.

Woods won his third Claret Jug in 2006 at Hoylake in 18-under par. McIlroy is 12 under through two rounds, four shots clear of Dustin Johnson, who shot a sterling 65 on Friday to keep McIlroy in his sights.

Perhaps most important to McIlroy’s psyche, though, is how definitively he exorcized the demons of Friday second rounds.

“I didn’t have that in my head at all,’’ McIlroy insisted — incredibly without a “just-kidding’’ wink-wink.

“It’s understandable,’’ McIlroy said. “People ask you. My second rounds this year have been terrible, and there isn’t really any explanation. But hopefully I put it to bed.’’

Graeme McDowell, mocking the Friday demons issue, said of McIlroy: “Any more questions about Friday? I saw the stat this morning, 43-under par on Thursdays and is 11-over on Fridays or whatever. Last week in you look at the Scottish Open, very difficult conditions on Friday. It’s always tough to back up good first rounds.

“He certainly put any demons that might have been there, he certainly put those to bed today. You run out of superlatives when you’re describing the kid’s game. He’s unbelievable. And no one will be surprised if he addresses the third leg of the Grand Slam this weekend.’’

If McIlroy can win this week, he would need only a Masters victory for a career Grand Slam.

After McIlroy at 12-under and Johnson at 8-under are six players at 6-under: Rickie Fowler, Sergio Garcia, Francesco Molinari, Ryan Moore, Charl Schwartzel and Louis Oosthuizen. Jim Furyk, Marc Warren and George Coetzee are at 5-under.

Phil Mickelson is even par and Tiger Woods made the cut on the number at 2-over.

As for McIlroy, his only goal was to “play another solid round of golf, stick to my game plan, stick to doing what I do well, which is take advantage of the par 5s.’’

He did just that, hitting his driver beautifully and letting his game flow from there.

“It’s not a surprise,’’ Woods said of McIlroy’s lead. “He’s done this before. He’s won I think both of his majors by eight, I believe. Once he gets going, he can make a lot of birdies and he plays pretty aggressively to begin with. And when he’s going, he can get it going pretty good.’’

It will be up to the rest of the field to chase him, because McIlroy was candid about the fact he has a similar feel to him this week that he had when he won his U.S. Open at Congressional and the PGA Championship at Kiawah Island.

“It’s just I feel like I have an inner peace on the golf course,’’ McIlroy said. “I just feel very comfortable. I’m very comfortable in this position. I’m very comfortable doing what I’m doing right now. It’s hard to describe. I wish I could get into it more often.

“People call it ‘the zone,’ people call it whatever, it’s just a state of mind where you think clearly. Everything seems to be on the right track. I’ve always said, whenever you play this well, you always wonder how you’ve played so badly before. And whenever you’ve play so badly, you always wonder how you play so well. Golf is a very fickle game. I’m happy where my game is at the minute, and hopefully I can just keep up the solid play for another couple of days.’’